Embolic stroke is a leading cause of death and disability among adults. The most common cause of embolic stroke emanating from the heart is thrombus formation due to atrial fibrillation (AF). AF is an arrhythmia of the heart that results in a rapid and chaotic heartbeat, producing decreased cardiac output and leading to irregular and turbulent blood flow in the vascular system.
In the case of patients who exhibit AF and develop an atrial thrombus, clot formation typically occurs in the left atrial appendage (LAA) of the patient's heart. The LAA is a small cavity formed within the lateral wall of the left atrium between the mitral valve and the root of the left pulmonary vein. In normal hearts, the LAA contracts in conjunction with the rest of the left atrium during the cardiac cycle; however in the case of patients suffering from AF, the LAA often fails to contract with any vigor. As a consequence, blood can stagnate within the LAA, resulting in thrombus formation.
Elimination or containment of thrombus formed within the LAA offers the potential to significantly reduce the incidence of stroke in patients suffering from AF. Pharmacological therapies, for example the oral or systemic administration of anticoagulants such as warfarin, are often used to prevent thrombus formation. However, anticoagulant therapy is often undesirable or unsuccessful due to medication side effects (e.g., hemorrhage), interactions with foods and other drugs, and lack of patient compliance.
Invasive surgical or thorascopic techniques have been used to obliterate the LAA, however, many patients with AF are not suitable candidates for such surgical procedures due to a compromised condition or having previously undergone cardiac surgery. In addition, the perceived risks of surgical procedures often outweigh the potential benefits.
Recently, percutaneous occlusion implants for use in the LAA have been investigated as alternatives to anticoagulant therapy. However, these implants are relatively non-conforming. Due to the non-uniform shape of the LAA, existing implants cannot completely seal the opening of the LAA in all patients. As a consequence, approximately 15% of patients receiving these implants experience incomplete LAA closure, necessitating prolonged treatment with anticoagulants. The anatomy of the left atrium and LAA of some patients also precludes the use of such implants. In addition, the occlusion implants can also cause life-threatening perforations of the LAA during the placement procedure.
More effective methods of occluding cavities or passageways in a patient, in particular cavities or passageways in the cardiovascular system of a patient, such as the LAA, offer the potential to improve patient outcomes while eliminating the undesirable consequences of existing therapies.